The present invention relates generally to the field of computed tomography (CT) imaging systems and specifically to source and detector configurations for stationary CT systems to facilitate measurement of more complete data for image reconstruction.
Computed tomography is a technique which creates two-dimensional cross-sectional images or three-dimensional volumetric images from three-dimensional structures. The CT imaging system primarily includes a CT gantry and a patient table or a couch. The gantry is a moveable frame that contains an X-ray source, which is typically an X-ray tube including collimators and filters on one side, and detectors with an associated data acquisition system (DAS) on an opposite side. The gantry typically also includes rotational components requiring slip-ring systems and all associated electronics, such as gantry angulation motors and positioning laser lights.
In known, so called “third generation” CT systems (source and detector configured in a fixed arrangement that itself either rotates or is combined with a device that rotates the object of interest), the X-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged, so that the angle at which the X-ray beam intersects the object constantly changes. As mentioned, X-ray sources typically include X-ray tubes, which emit the X-ray beam from a focal spot. An X-ray detector may include a crystal or ionizing gas that, when struck by an X-ray photon, produces light or electrical energy. The three exemplary types of detectors utilized in CT systems are scintillation, gas ionization, or direct conversion detectors. The CT systems may typically include post-patient collimators for reducing scattered radiation at the detector. These systems have limitations regarding rotational speeds, mechanical balancing of the systems, power and thermal requirements, which become increasingly complex due to the rotational components.
Other types of CT architectures, which include stationary CT designs, offer high scanning speeds, and incorporate mechanisms for directing a high-intensity electron beams onto stationary X-ray targets to produce X-rays (electron-beam CT systems). There are, however, challenges with respect to acquiring more complete image data in these stationary CT configurations. In stationary CT systems of the type described above, both the X-ray source and the detector are stationary, circling either the entire gantry or a substantial part of the gantry.
An alternative stationary CT system design includes a distributed X-ray source that either encircles the entire gantry or is of sufficient extent to facilitate imaging scenarios. The X-ray source is typically comprised of several discrete electron emitters. Since both the X-ray source and detector are stationary in stationary CT configurations, they need to be designed to facilitate appropriate scanning protocols. In a preferred axial scanning configuration, the distributed X-ray sources at both longitudinal extents of a centered detector may be slightly offset (vertically and/or radially) relative to the area detector array. As a result, a volume in the center of the field of view of the imaging system is not subjected to X-rays, prohibiting reconstruction in this volume. In a preferred helical scanning configuration, a distributed X-ray source is placed between two area detectors that circle the entire gantry. The X-rays are emitted through a gap between the two detector arrays to administer X-ray flux to the imaging volume. Because the X-ray source is also distributed around the entire gantry, the gap encircles the entire gantry, which prohibits measurement of CT projection data and artifact-free image reconstruction within the corresponding volume.
It is therefore desirable to provide improved source and detector configurations for stationary CT systems to facilitate measurement of more complete data for image reconstruction.